1. Field of the Invention
This invention relates to a technique and instruments for performing orthopedic surgeries such as total hip arthroplasty. This technique allows a long bone, such as a femur, to be prepared to receive a prosthesis, such as a total hip replacement, by reaming a lateral bore, in the bone, until the isthmus using a series of reamers on a flexible shaft and then reaming the calcar region of the bone. The invention specifically relates to a combination of specially shaped remers that match the prosthesis shape and a flexible shaft that provides control, and allows the reamers to be angled in a controlled manner to shape the bone canal to fit the prosthesis line-to-line.
2. Description of the Prior Art
Surgeons strive for accurate, replicable surgical techniques so that precise fits can be obtained between the prosthesis and bone. It is believed that in a non-cemented application a precise fit enhances prosthesis life. This increased contact area between bone and prosthesis has been shown to improve long-term fixation. Accurate bone preparation for cemented prostheses will also provide improved long-term fixation due to precise and optimal cement mantle thickness between bone and the prosthesis.
There has been a growing movement in the orthopedics community to move away from bone preparation that involves introducing large impact forces from hammer blows. Current surgical bone preparation technique involves shaping the bone by introducing a broach or rasp type device with a hammer. This can result in large dynamic stresses within the bone, which has been known to crack or deform the bone in some cases. Even with this drawback, broaching is widely used because it allows for very irregular, non-symmetric shapes for non-symmetric prostheses to be formed in bone. The broach is shaped exactly like the prosthesis with an appropriate gap or undersize condition for interference fit accounted for and impacted into a bone cavity that has been initially opened with straight or tapered reamers.
The traditional or current approach to forming the bone envelope for total joint replacement is generally termed a three step process, excluding the ostectomy, with multiple iterations per step. First a series of distal reamers are passed into the isthmus, swing up on each pass until cortical contact is felt. Next, a series of tapered mid-shaft or conical reamers are introduced in incremental sizes to shape the mid-shaft portion of the bone and to remove proximal lateral bone and to notch the greater trochanter to ensure neural alignment. Lastly, a series of incrementally sized broaches are impacted into the bone to remove proximal medial bone and to clean up any remaining bone from the lateral and distal areas. Leaving so much bone behind for the broaches to remove results in much hammering and impact stresses in the bone. So much so, that some surgeons have been known to do a prophylactic cerclage of the proximal bone with either wire or a clamp to prevent cracking while impacting the broach. The instruments required for this technique include two or three distal reamers, two tapered mid-shaft reamers, two broaches--broach handles/impactor extractors and hammers and an optional prophylactic cerclage device.
Commercially available jigs for off-axis reaming are not able to ream curves, rather than angles, around corners nor are they able to control the sizing and alignment of the medullary canal.